We report on properties of hadronic events from e + e − annihilation observed by the ALEPH detector at the large Electron Positron Collider at CERN. The center-of-mass energy was s =91.0−91.3 GeV . Measured distributions of the global event-shape variables sphericity, aplanarity, thrust and minor value, and of the inclusive variables x p , p ⊥ in , p ⊥ out and y are presented. We measure a mean charged multiplicity in hadronic events of 〈 N ch 〉=21.3±0.1 (statistical)±0.6 (systematic). The data are in good agreement with QCD-based models which use the leading-logarithm approximation, and are less well described by a model using O( α s 2 ) QCD.
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Measurements are presented of the variation with Q 2 (scaling violation) of the hadron multiplicity in deep inelastic muon-proton scattering. An increase in the average multiplicity of both the charged hadrons and K 0 mesons is observed with increasing Q 2 or x Bj for fixed centre-of-mass energy W . The study of the shape of the effective fragmentation function D h ( z , W , Q 2 ) shows that the increase of the particle yield with Q 2 takes place for low z particles. The variation of the hadron distributions with Q 2 is also studied in the current fragmentation region where a decrease in multiplicity is observed. Such effects are expected from QCD.
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Properties of the hadron multiplicity distributions in 280 GeV/c μ<sup loc="post">+</sup>p interactions have been investigated. The c.m. energy dependence in the range from 4 to 20 GeV of the total charged multiplicities are presented. No variation faster than logarithmic is seen in the energy range of this experiment. Comparison with νp and <math altimg="si1.gif"><ovl type="bar" style="s">ν</ovl><rm>p</rm></math> data at lower energy has been made and shows good agreement between μ<sup loc="post">+</sup>p and <math altimg="si1.gif"><ovl type="bar" style="s">ν</ovl><rm>p</rm></math> total charged multiplicities. It has been found that the average forward multiplicity (charged hadrons with xF > 0) exceeds the average backward multiplicity (charged hadrons with xF < 0) in the whole energy range and presents a different energy variation. The average forward multiplicity has been compared to e<sup loc="post">+</sup>e<sup loc="post">−</sup> data and shows a similar dependence on energy. Little correlation was observed between the forward and backward multiplicities indicating that the current and target regions fragment almost independently.
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Backward Multiplicity.
Forward Multiplicity.
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The inclusive production cross sections and mean multiplicities of π±, K±, p, and p¯ in e+e− annihilation at a c.m. energy of 29 GeV have been measured with the time-projection chamber at PEP, using ionization energy loss to separate particle types. On average, 10.7±0.6 π±, 1.35±0.13 K±, and 0.60±0.08 p,p¯ are contained in an annihilation event. The fraction of pions among final-state particles decreases from over 95% at 0.3 GeV/c momentum to about 60% at high momentum; the kaon and proton fractions rise correspondingly.
PARTICLE FRACTIONS.
PARTICLE FRACTIONS.
PARTICLE FRACTIONS.
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